1. Field of Invention
The present invention relates generally to fluid dispensing utensils and, more particularly, to a fluid dispensing utensil which is adapted to prevent leakage.
2. Description of the Related Art
Fluid dispensing utensils are commonly used to deliver fluids such as ink, paint, adhesives, shoe polish, lotion, medicine, perfume, makeup, white out and food. In one type of fluid dispensing utensil, a relatively large volume of fluid is stored in a non-capillary container (or reservoir) where it is allowed to move freely. Pens which incorporate such a container, for example, are referred to as "free ink" pens. That is, the ink in the reservoir is usually in a liquid state, and is free to move about as the writing utensil is moved. Fluid in these utensils is transferred from the container to the delivery end (often referred to as a tip or a nib) via a capillary conveying line. A slight vacuum (underpressure) relative to the atmosphere is maintained within the container which prevents fluid in the conveying line from escaping from the utensil until the tip is brought into contact with the surface onto which fluid is to be dispensed. At this point, the force of attraction of the surface and the capillary force of the space between the surface and portions of the tip which are not in direct contact with the surface will cause the fluid to flow from the tip to the surface. As fluid is dispensed, air enters the container in a controlled manner via a precisely sized air inlet that is formed in the container and ends within the fluid. The air replaces the fluid so as to maintain the vacuum at a relatively constant level.
One problem associated with these dispensing devices is leakage caused by air expansion within the container. Specifically, when the air within the container is heated it expands. This causes the vacuum within the container to subside and increases the vapor pressure on the fluid. The reduced vacuum and increased vapor pressure cause the utensil to leak through the tip when oriented in the delivery orientation, i.e. when facing at least partially downwardly.
In an attempt to reduce these types of leaks, some ink pens include an overflow chamber having a capillary storage that will absorb ink. Fountain pens, for example, include a capillary storage in the front section and sometimes under the nib. This storage has a capillarity that is strong enough to prevent leakage when the pen is held in the writing position, but not so strong that it will be filled during a normal writing operation. The capillary storage will not receive fluid when there is substantial air expansion within the container. As a result, these capillary storage systems have been unable to prevent leakage from free ink pens which hold a relatively large volume of ink and, ultimately, a relatively large volume of air. They have also been unable to prevent the leakage caused by relatively large amounts of air expansion in smaller containers.
The storage capacity of existing fountain pen systems which are able to prevent leakage during temperature fluctuations associated with normal use is less than 2.0 milliliters. The reasons for this limitation are as follows. The conveying tube, which transfers fluid via capillary action, must be large enough to produce the desired ink flow during writing. The capillary storage consists of capillaries that must be larger than those of the conveying line. Otherwise, the storage would normally be filled with ink and unable to store excess ink as needed. The storage must also create enough capillary force to hold the ink when the fountain pen is being held vertically. Such force (which is often referred to as "capillary height") is inversely related to the size of the capillaries. Thus, in order to increase the volume of the storage, it is necessary to reduce the size of the capillaries. This is not possible, however, because the storage capillaries must be larger than those of the conveying line, which in turn must be large enough to insure proper ink flow. Accordingly, the volume of liquid that can be stored by the capillary storage is limited. This limits the amount of ink that can be stored in the reservoir.
Other pens include capillary storages configured such that the vast majority of the pores are smaller than the air inlet and are made of a material that is the same or substantially similar to that which forms the conveying line. As a result, the capillary storage will normally be completely filled with fluid and unable to receive additional fluid when air expands within the container. One proposed method of reducing this problem is to reduce the size of the air inlet. The proposed method has proven to be unsuccessful, however, due to manufacturing limitations which make it prohibitively difficult to produce sufficiently small air inlets. Another proposed method of reducing this problem is to increase the size of the storage capillaries. This method has also proven unsatisfactory because the increase in pore size decreases the capillary height of the capillaries and reduces the amount of fluid that can be stored therein when the pen is in the upright position. Thus, to optimize the performance of the conveying line and the storage capillaries, the pore sizes of the conveying line and storage capillaries are preferably carefully controlled.
Still other pens include capillary storages that consist of a series of radially extending fins which form capillaries therebetween. There are a number of disadvantages associated with the fin-type capillary storages. For example, air interferes with the flow of ink back to the reservoir. In addition, fin-type capillary storages take up a relatively large portion of the overall volume of the pen, thereby substantially reducing the amount of volume available for the ink reservoir.
Yet another problem is that the capillary storage swells as it absorbs the excess fluid. The swelling causes the capillary storage to push against the container wall, thereby restricting the air within the capillary storage from releasing freely into the atmosphere, through the surface areas where the storage member pushes against the container wall. The trapped air within the capillary storage, however, prevents the capillary storage from absorbing additional excess liquid. Thus, the swelling limits the capillary storage from absorbing to its full capacity.